A glacier in West Antarctica is flowing much faster than its neighbor and “stealing” its ice – an important discovery for a better understanding of Antarctica’s contribution to sea level rise.
High-resolution satellite images of the Pope, Smith, and Kohler Glacier (PSK) region, located in the immediate vicinity of the “doomsday glacier” Thwaites, have revealed a surprising phenomenon: the eastern stream of the Kohler Glacier is tapping ice from its neighbor, the western Kohler Glacier stream. The research team from the University of Leeds refers to this as “ice piracy”.
However, the researchers highlight the short period of time in which they observed this process as the real sensation. What was previously assumed to be a slow process over centuries or even millennia has now been documented by the researchers in just 17 years. The Kohler East Glacier gained significant speed during this time, while the Kohler West Glacier slowed down.
The study, led by the University of Leeds and published in The Cryosphere on May 8, is based on data from the Copernicus Sentinel-1 satellite and many years of ice movement measurements. It aimed to investigate the change in flow speed and direction of eight glacier streams in the PSK region – particularly with regard to their contribution to the Crosson and Dotson ice shelves.
For the period between 2005 and 2022, the scientists analyzed how regional acceleration and thinning of the ice influence ice transport into these ice shelves. The position of the calving fronts was also tracked over 15 years (from 2005 – 2020). The results indicate that the dynamics of individual glacier streams can also destabilize neighbouring systems.
Their analysis shows that seven of the eight glacier streams examined in the region have accelerated considerably at the grounding line – the transition from fixed glacier to floating ice shelf – in these 17.5 years, by an average of 51 percent. Similar developments have also been observed in other Antarctic glaciers as a result of climate change. If the grounding line retreats, it can lead to the destabilization of the glacier and further accelerate the flow of ice towards the ocean.
In 2022, six of the ice streams even reached average flow velocities of more than 700 meters per year. The research team observed the highest acceleration over the 17.5 years in the directly adjacent glaciers Kohler East and Smith West; both flowed around 560 meters faster per year in 2022 than in 2005.
What is surprising, however, is that the ice flow of the Kohler West Glacier slowed by ten percent in the same period – presumably triggered by the loss of ice to its neighbor Kohler East.
“We think that the observed slowdown on Kohler West Glacier is due to the redirection of ice flow towards its neighbour – Kohler East. This is due to the large change in Kohler West’s surface slope, likely caused by the vastly different thinning rates on its neighbouring glaciers,” explains Dr. Heather Selley, researcher at the School of Earth and Environment at the University of Leeds and lead author of the study, in a university press release.
The researchers also found that the change in ice flow direction and associated “piracy” from the Kohler West Glacier has altered the amount of ice flowing into the Crosson and Dotson ice shelves to an extent not previously observed. According to Anna Hogg, professor of Earth Observation in the School of Earth and Environment at the University of Leeds and co-author of the study, this likely plays a significant role in maintaining Dotson and accelerating the deterioration of Crosson.
The flow rate of the ice – and how quickly it ultimately melts in the ocean – is crucial for its influence on sea level rise.
“Our results suggest that ice flow redirection is an important new process in contemporary ice-sheet dynamics, which is required to understand present-day structural change in glaciers and the future evolution of these systems,” says Prof. Hogg in an ESA news release.
The new observations show interactions between floating ice shelves and the overlying ice sheet that were previously little understood – and could have a direct impact on the development of global sea levels in the 21st century.